CLEANUP: .gitignore: ignore more test files

Exclude from "git status" many of the files that often result from
development tests and bug reports reproducers.

.gitignore

@@ -18,3 +18,31 @@ make-*
 dlmalloc.c
 00*.patch
 *.service
+*.bak
+.nfs*
+contrib/base64/base64rev
+contrib/halog/halog
+contrib/ip6range/ip6range
+contrib/iprange/iprange
+tests/test_hashes
+/*.cfg
+/*.conf
+/*.diff
+/*.patch
+/*.c
+/*.o
+/*.so
+/*.txt
+/*.TXT
+/*.txt.*
+/*.prof
+/*.gprof
+/*.prof.*
+/*.gprof.*
+/*.tar
+/*.tar.gz
+/*.tgz
+/*.mbox
+/*.sh
+/bug*
+/TAGS